SIMBAD references

In a disk around DM Tau, previous observation of ¹³CO (J=2-1 and 1-0 transitions) derived a ¹³CO gas temperature of ∼13-20 K, which is lower than the sublimation temperature of CO (20 K). We argue that the existence of such cold CO can be explained by a vertical mixing of disk material. As the gas is transported from a warm layer to a cold layer, CO is depleted onto dust grains with a timescale of ∼10³ yr. Because of the steep temperature gradient in the vertical direction, an observable amount of CO is still in the gas phase when the fluid parcel reaches the layer of ∼13 K. Apparent temperature of CO decreases as the maximum grain size increases from micron to millimeter size.